Process for the production of perborates

ABSTRACT

This invention relates to a process for the production of perborates by the reaction of dried borates, the particles of which have an inner surface area of at least 0.4 m2/g, with hydrogen peroxide in an organic solvent.

United States Patent 1 Flatz 1 Feb. 27, 1973 PROCESS FOR THE PRODUCTIONOF PERBORATES [75] Inventor: Wolfgang Flatz, Basel, Switzerland [73]Assignee: Sandoz Ltd., Basel, Switzerland 22 Filed: July 6, 1970 [21]App1.No.: 52,755

[30] Foreign Application Priority Data July 29, 1969 Switzerland 11519/69 Sept. 5, 1969 Switzerland ..13484/69 Sept. 10, 1969 Switzerland..l3650/69 [52] US. Cl ..423/281 [51] Int. Cl. ..C0lb 15/12 [58] Fieldof Search ..23/59, 60

[56] References Cited UNITED STATES PATENTS 2,623,856 12/1952 Sanders..23/59 x 3,309,170 3/1967 Griswold ..23/59 3,454,357 7/1969 Rhees eta1. ..23/59 X 2,097,411 10/1937 Corkill ..23/59 3,336,103 8/1967Schumacher et a1. ..23/59 FOREIGN PATENTS OR APPLlCATlONS 1,504,84810/1967 France ..23/60 Primary Examiner-Herbert T. Carter Att0rney--G.D. Sharkin, T. C. Doyle, R. S. Honor, W. F. Jewell, T. O. McGovern, R.E. Vila and F. H. Weinfeldt [5 7] ABSTRACT This invention relates to aprocess for the production of perborates by the reaction of driedborates, the particles of which have an inner surface area of at least0.4 m lg, with hydrogen peroxide in an organic solvent.

5 Claims, No Drawings PROCESS FOR THE PRODUCTION OF PERBORATES Thisinvention relates to a process for the production of perborates by thereaction of borates, the particles of which have an inner surface areaof at least 0.4 m lg, with hydrogen peroxide in an organic solvent.

It is known, for example from Belgian Patents 681,366 and 689,834, thatperborates, preferably sodium perborate, can be obtained by reactingdried borates with hydrogen peroxide in an organic solvent. It isimportant that the reaction should be carried out in the presence ofvery small amounts of water. The water may be bound to the borate in theform of water of crystallization or crystal water, or it may bedissolved in the organic solvent. Dried sodium metaborate is widely usedto produce perborates by this process.

The tetrahydrate crystallizes from aqueous solutions of sodiummetaborate at temperatures around 20C. Hitherto the dihydrate has beenobtained from this product by drying at temperatures up to 90C and theless hydrated products by drying at temperatures above 90C. In this way,however, complete dehydration of sodium metaborate is practical only attemperatures higher than 250C. In this drying technique the crystalwater escapes very slowly and the dried product does not differmaterially from the starting product in its inner surfacecharacteristics, nor, consequently, in the bulk density. For this reasonone known process on an industrial scale makes use of crystallizers,mechanical dehydrating devices and a calcining oven. In another processsodium metaborate solutions are heated until no more than 2 moles ofwater per mole of borate are present; the solution, or more properly themelt, is then cooled on a drum and allowed to solidify. The borates thusobtained have a water content invariably greater than 1.75 moles P1 permole NaBO Thirdly and lastly, sodium metaborates containing 1 to 4moles'of crystal water per mole of borate are produced by sprayingstoichiometric amounts of aqueous sodium hydroxide solution on sodiumtetraborate, which does not however yield a product of homogeneouschemical composition. These known processes invariably result inproducts of very coarse grain, which usually have to be ground beforefurther use. After grinding, the product is always found to have a grainspectrum of very wide size distribution, with compact discrete grains.

Since the reaction of sodium borates with hydrogen peroxide takes placeon the crystal surface of the borate, attempts have been mode to attainto the optimum in reaction speed and yield of high-percentage borate bysuperfine grinding of the borate. As yet, this approach has not led totechnically satisfactory reaction times.

An attempt has now been made to produce sodium metaborate with a maximumcrystal water content of 2 moles H O per mole of NaBO by drying anaqueous solution of sodium metaborate in an atomizer, where the solutionis sprayed into a stream of hot gas, with the aim of obtaining productsof greater inner surface area. These trails resulted in light-weightproducts with a content of crystal water between the lower and upperlimits of approximately 0.25 mole and 1.1 moles H O per mole of NaBO Theinner surface area of these atomizer dried borates is generally greaterthan 1 mlg;

values of the order of 1.5 to 2.5 m /g are attainable with ease.

By using contact heat for drying sodium metaborate, with the applicationof vacuum, products with an inner surface area of 0.5 0.7 m /g arereadily obtainable. Cyclone driers are capable of yielding homogeneousproducts with a larger inner surface area.

The conditions in the drying of commercial borax and the other borateswhich can be used for producing perborates are similar to those formetaborate.

It has now been found that borates with an inner surface area greaterthan 0.4 m lg are particularly well suited for the production ofperborates by the process in which an organic compound containing atleast two hydrogen atoms oxidizable with the formation of hydrogenperoxide is oxidized in an organic solvent or solvent mixture andsimultaneously or subsequently reacted with solid borates in thepresence of small amounts of water. Borates with an inner surface areabetween 1.5 and 2.5 m /g are especially suitable.

Products with such a large inner surface area react more rapidly withhydrogen peroxide in organic solvents than the finely divided boratesobtained by grinding. In the same reaction time these very finelydivided, usually scaly products form perborates in substantially higheryield; as an associated effect the amounts of decomposition products aresmaller, which is important for recovery of the solvent; and finally theperborates are less subject to discoloration than perborates producedfrom borates of higher bulk density.

For drying by the atomizing technique, sodium metaborate solutions witha concentration of about 1.8 to 10 moles of water per mole of borate canbe used, although it is economically of advantage to work with solutionsof concentrations of 2.5 to 4 moles of water per mole of borate. It isbest to prepare the solution by evaporation of a dilute solution, andthe normal practice is to run it hot into the atomizer drier, i.e., attemperatures in the region of C. The atomizer must therefore be a typedesigned to accommodate solutions and melts at temperatures of about C.

The crystal form of the resulting sodium metaborate depends on thetemperature of the stream of hot gas which, as previously stated, isdirected through the reaction mixture. If the gas temperature is higherthan about 150C on entry and above about C on exit, crystals of scaly,fissured structure are normally obtained. These products therefore havea very large surface area and, accordingly, a low bulk density, which isgenerally less than 0.3 g/cm and is optimally of the order of 004-01glcm The grain size of these coarse blown products is in the region of 1cm diameter. They are very hydroscopic.

If the starting product is sodium tetraborate it is advantageous toprepare the solution at a concentration of at least 10 moles of waterper mole of tetraborate; about 200 moles of water per mole oftetraborate can be given as the upper limit. For economical operation,however, a concentration of 21 to about 60 moles of R 0 per mole ofNazB407 is best. These solutions can be prepared, for example, by addingwater to a commercial grade of tetraborate and filtering'the solution.They can be conveyed hot into the atomizer drier, i.e., at temperaturesfrom about 40C to about C.

The stream of gas used in the process can be passed through parallelwith the path of exit of the liquid from the nozzle, or in the oppositedirection. Normally few specifications are made fro the gas; its mixturecontent should be low and it should be free from dust. In fullscaleproduction of stream of hot air, filtered if necessary, is sufficient.If a product with a range of small grain sizes is desired, as isgenerally the case, the hot gas jet can be directed into the batch sothat a vortex is created in which the solid grains collide against eachother and the walls of the machine and are broken down by attrition(comminution in a cyclone and/or with pneumatic promoting effect).Generally, these conditions give rise to a product of small grain sizeand even size distribution. A series of such trials yielded a productwith an arithmetic mean grain size of less than 40 microns and agranulation parameter 11 greater than 2.1, more specifically about 2.3(determinations as in German Industrial Standard 4190, Draft of March1966).

EXAMPLE 1 A solution of sodium metaborate in water (in the ratio of 4moles of H to 1 mole of NaBO heated to about 95C, is conveyed through astandard atomization apparatus into an atomizer drier. Air at an entrytemperature of 200C is passed through in the same direction as the pathof flow of the solution, the temperature of the spent air being 150C. Apuffy product resembling snowflakes is formed which is of low bulkdensity and has a crystal water content of 0.6 moles 11 0/1 mole NaBOHaving passed a cyclone, a product is obtained with a bulk density of 52kg/m and an inner surface area of 1.8 m /g.

EXAMPLE 2 A solution of sodium metaborate in water (2.9 moles of H 0 to1 mole of NaBO at about 95C is fed through an atomizing apparatus intoan atomizer drier. The entry and exit temperatures of the air are 190and 140C, respectively, and its direction of flow is parallel to that ofthe solution. At the end of the drying zone cold air is blown in to coolthe product and break down the grains by attrition. A very fine finalproduct is obtained which contains 0.8 mole of crystal water per mole ofsodium metaborate. Its bulk density is 65 kg/m and its inner surfacearea 1.0 m /g.

is directed through an atomizing apparatus into an atomizer drier, wherea countercurrent of air, entry temperature 600C, exit temperature 370C,is passed through it. A puffy product like snowflakes is formed. Aftercomminution in cyclone it is obtained with a bulk density of 30 kg/m, aninner surface area of3.5 m lg, a water content of 0.56 mole H O per moleof Na B O and a mean grain size of about 37 microns.

EXAMPLE 7 An aqueous solution of sodium tetraborate (23 moles H O to 1mole Na B O-,) at about C is conveyed through an atomizer and atomizerdrier. A stream of air is injected at 310C to pass through in the samedirection as the solution and escape at 210C. After comminution in acyclone a very fine product is obtained containing 1.2 moles 11:0 to 1mole Na B O The bulk density of this sodium tetraborate is 45 kg/m andits inner surface area 2.9 m /g.

EXAMPLE 8 A solution of sodium tetraborate in water (33.8 moles H O to 1mole Na B O,) at about 85C is directed through an atomizing apparatusinto an atomizer drier. A stream of air enters at 210C and escapes atabout C after passing through the solution in the concurrent direction.The dried tetraborate is comminuted in a cyclone, which gives a veryfine product containing 2.2 moles of H 0 per 1 mole of Na B O? Its bulkdensity is 85 kg/m and the inner surface area 0.6 m /g.

EXAMPLE 9 A solution of parts by weight containing 0.297 mole of2-ethylanthrahydroquinone, 0,103 mole of 2- ethylanthraquinone and 0.290mole of water per kilogram is prepared with acetic cyclohexylester assolvent. The solution is circulated and 3.49 parts of a sodiummetaborate produced by spray drying are entered. The resultingsuspension is treated with an air current at a reaction temperature of52C. The rate of flow of the air is 520 N1 /hour and its moisturecontent is calculated so that the water content of the solution remainsconstant. The starting sodium metaborate contains per mole 0.70 mole ofwater (analytical value 12.77 gram atoms sodium per kilogram), its innersurface is 1.6 m lg. After 20 minutes reaction time the solid isseparated, since the circulated solution then contains only 0.006 moleof hydrogen peroxide per kilogram. The solid is filtered, the filtercakewashed several times Further trials were enrrietl out as deserihed inExample 1, the differences relative to that Ilxrnnple. being as follows:

'leinpern Water ('uuleul. 'lein wrnlnre, (1. Inner ture nf olsnlutlnu. VV Ilulk surluse lCxmnple sulllliou, mules 1120/ lnemuin z Spent density,area, No. nmles Nam): air air Water content All How kL'./lll. mJ/g.

3.. 110 4 150 1110 1.1 mole per Concurrent 85 0.0

mole. N11130: -l 110 l l; 3110 .200 0.4 mole per Concurrent 40 2.!)

mole N21130: 5 110 2. is (100-4160 270 0.3111010 per Counter- 32 3. 5

mole current NflBOz EXAMPLE 6 with benzene and freed from adheringresidual benzene At about 100C a solution of sodium tetraborate in water(in the rate of 23.1 moles of H 0 to 1 of Na B O by short evacuation.The yield is 4.66 parts ofa product containing 9.55 gram atoms of sodiumand 9.28 gram atoms of hydrogen peroxide, which is equivalent to 14.8percent active oxygen. In relation to the starting 2-ethylanthrahydroquinone this corresponds to a yield of about 97 percentand a loss of aBout 1 percent.

COMPARATIVE EXAMPLE A sodium metaborate is dried at 250C in a dryingcabinet to 0.70 mole H 0 per mole of borate (analytical value 12.75 gramatoms of sodium per kilogram) and ground to a mean grain size of 45microns. 3.49 parts of this sodium metaborate are reacted by theprocedure and under the condition of Example 9. This results in 4.09parts of the product containing l0.88 gram atoms of sodium and 6.87 gramatoms of hydrogen peroxide, which is equivalent to an active oxygencontent of 11.0. Relative to the starting 2- ethylanthrahydroquinone,this corresponds to a yield of approximately 63 percent and a loss ofabout 6 percent.

Approximately the same results are obtained when the sodium metaborateis added to the solution after its air treatment.

Having thus disclosed, the invention what I claim is:

1. In a process for producing perborate wherein an organic compound,containing at least two hydrogen atoms oxidizable with the formation ofhydrogen peroxide, is oxidized in organic solvent and reacted with solidborate in the presence of a small amount of water, the improvementwherein the borate is spray dried perborate precursor having an innersurface area greater than 0.4 m lg and a content of crystal waterbetween 0.25 and 1.1 mole of borate.

2. A process according to claim 1 wherein the borate has an innersurface area between 1.5 and 2.5 m lg.

3. A process according to claim 1 wherein the borate is a metaborate.

4. A process according to claim 1 wherein the borate is borax.

5. A process according to claim 1 wherein the borate has an arithmeticmean grain size of less than 40 microns.

2. A process according to claim 1 wherein the borate has an innersurface area between 1.5 and 2.5 m2/g.
 3. A process according to claim 1wherein the borate is a metaborate.
 4. A process according to claim 1wherein the borate is borax.
 5. A process according to claim 1 whereinthe borate has an arithmetic mean grain size of less than 40 microns.